Motor Junkie article spreads FUD: "20 Drawback Of Electric Vehicles Drivers Commonly Overlook"

ajdelange

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What if someone just wants the 105KW or the 135KW battery?
Then he will have to live with the consequences of his decision.


I believe the infrastructure should be improved to allow those people to make that journey too.
I think everyone agrees that better charging infrastructure is a thing to be devoutly wished. Just read an article that says charging infrastructure has replaced range anxiety as No. 1. on the list.

The EPA rating is not for pure highway driving, it is for a combination of city and highway. EVs get better range in slower stop and go traffic than on the highway.
Uh, no. Not in my experience anyway. And the physics says more or less the same thing. It is true that regen recovers much of the intertial load (which is the biggest load in town) but not all of it. Now I should point out that where I live the freeway traffic is pretty bad so that there is a fair amount of stop and go on the freeway too.


I did a trip recently to Tucson from Phoenix at highway speed (75 MPH in AZ) and the headwind was 20-30 MPH. My range dropped to 170 miles.
(75 + 30)/75 = 1.4, almost the square root of 2. Thus your drag will be doubled and if you are driving in a place where you can cruise at 75 you are not driving in a place where you are speeding up and slowing down a lot. Drag dominates inertial and is your biggest load. Did you expect otherwise?

If there is a message here for other readers it is that you have to pay attention to this. When drag dominates your range will go down. Drag load is not recovered by regenerative braking. I admittedly am somewhat dismissive with regard to this because I used to fly small airplanes and this sort of thing is very familiar to me. When there is a headwind a pilot knows to take that into account in his planning. But don't worry. The Rivian is almost 100% certain to have tools that will make this planning or, if it comes up unexpectedly, tell the driver what to do. In a Tesla an alert appears that says "Slow down to below 65 to reach your destination" or something like that.


Many people may not want to choose the larger battery, in particular if they will make only 1 long range trip a year.
Life seldom rewards people with what they want just because they want it. One's choices lead to consequences.

The low end battery is fine for driving around town.
Then people who chose the shorter range versions should perhaps not plan to make long trips in them.


But if there were a CCS charger in Kingman ... it is just that this route is very popular in the southwest.
Then a DC fast charger will probably be built there before any of us sees his R1T.
 
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azbill

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Then he will have to live with the consequences of his decision.


I think everyone agrees that better charging infrastructure is a thing to be devoutly wished. Just read an article that says charging infrastructure has replaced range anxiety as No. 1. on the list.

Uh, no. Not in my experience anyway. And the physics says more or less the same thing. It is true that regen recovers much of the intertial load (which is the biggest load in town) but not all of it. Now I should point out that where I live the freeway traffic is pretty bad so that there is a fair amount of stop and go on the freeway too.


(75 + 30)/75 = 1.4, almost the square root of 2. Thus your drag will be doubled and if you are driving in a place where you can cruise at 75 you are not driving in a place where you are speeding up and slowing down a lot. Drag dominates inertial and is your biggest load. Did you expect otherwise?

If there is a message here for other readers it is that you have to pay attention to this. When drag dominates your range will go down. Drag load is not recovered by regenerative braking. I admittedly am somewhat dismissive with regard to this because I used to fly small airplanes and this sort of thing is very familiar to me. When there is a headwind a pilot knows to take that into account in his planning. But don't worry. The Rivian is almost 100% certain to have tools that will make this planning or, if it comes up unexpectedly, tell the driver what to do. In a Tesla an alert appears that says "Slow down to below 65 to reach your destination" or something like that.


Life seldom rewards people with what they want just because they want it. One's choices lead to consequences.

Then people who chose the shorter range versions should perhaps not plan to make long trips in them.


Then a DC fast charger will probably be built there before any of us sees his R1T.
I understand all about drag, I am an engineer who has worked in aerospace for over 40 years, and I also had a pilot's license. Yes drag goes up with the square of airspeed. That range drop was not unexpected. I am pointing this out because it is something that Rivian buyers should consider when selecting a battery size. In particular the R1S will not be available with the third row seat AND 180KW.

As for EPA ratings, my Bolt has an EPA range of 238 for normal driving, but it is rated at 213 for highway driving only. That is a 10% reduction, which is completely understandable considering increased drag and no regeneration. EPA highway assumes 65 MPH speed. That is a 10% reduction for highway driving and I expect similar numbers for the Rivian, especially since the front area for a truck is much more than a car. Every manufacturer claims great aerodynamics, but reality is the more frontal area, the more drag.

Another factor when living in the west is mountains, the climb from Phoenix to Flagstaff is 5000 feet. Fortunately Flagstaff has multiple DFDCs, EA and ChargePoint. Coming home is nice in that case, because there is regeneration.

I was actually the first paying customer that EA had in Arizona and I did a phone survey with them over two years ago. At that time I requested sites in the Blythe/Quartzsite area and also in Kingman. Today, the one in Quartzsite is finally marked as coming soon, but there is actually no construction yet. Experience has shown that EA sites take 6-9 months to complete. As of today, nothing is shown for Kingman, there is a huge gap along I-40 from Flagstaff to California and Nevada. I am setting my expectations low, I think it will be 2-3 years before that is covered.
 

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Sure and I once arrived in a town on fumes in an ICE vehicle where a freak, unseasonal, snowstorm had knocked out power and none of the gas stations could pump gas.
As Hurricane Irma was heading toward southwest Florida in 2017, gas station lines started forming several days out. Two days before Irma made landfall, there was no gas to be found anywhere. Once Irma hit, power was out -- along with gas pumps -- in much of the area for nine days. The few stations that could pump gas using generators were restricted to selling only to emergency vehicles.

I kept my Tesla charged using my home generator and was the only one among our friends who remained mobile throughout the period.

I'll probably keep an ICE vehicle until fast chargers become truly ubiquitous, but I will also never be without an EV going forward.
 

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As for EPA ratings, my Bolt has an EPA range of 238 for normal driving, but it is rated at 213 for highway driving only. That is a 10% reduction, which is completely understandable considering increased drag and no regeneration. EPA highway assumes 65 MPH speed.
Actually, the EPA hwy test cycle has an average speed of 48 mph with a top speed of 60 mph.
1595088200162.png


If GM used the 5 cycle test instead of the 2 cycle test, one of the additional cycles would be the "high speed" test. The average speed of this test is still 48, but it does hit 80 mph.
1595088346913.png


The Bolt got 310 miles on the hwy test. This number is derated by 30% to better reflect real world conditions.
https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=46153&flag=1

EPA ratings for the 1st gen Bolt are 255 City, 217 Hwy
 

Hmp10

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When I set my 2015 Tesla Model S cruise control to drive at 75 mph across Alligator Alley (a flat, straight, lightly-traveled stretch of I-75 across southern Florida), the car consumes 10 miles of indicated range for every 6 miles of actual road travel (measured by highway markers) in warm, dry weather.

EPA ratings are nowhere near realistic for prolonged driving on interstates . . . unless you don't mind rear-end collisions.
 

ajdelange

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I've always found them pretty good but I suspect I drive more conservatively than many of you do.
Here's some data on my last 80 drives (with Covid quarantines we just haven't been out much).

Graph0.jpg

Note that the drives (little circles) represent the consumption as a function of average speed for the drive. There is a little freeway at 65 and 70 but even so the average speed for the drives tend to be lower. Nevertheless the dominance of unrecoverable inertial in heavy traffic is plain and the v-squared dominance of drag at higher speed is at least hinted at. The heavy blue line represents the EPA overall estimate for my car (EPA range 351 miles - not subdivided into city and highway or if it is I don't have that data). As the data show I do get the EPA rated consumption sometimes, even up to 62 mpH average soeed, and sometimes I don't, even in town. Strong message to people for whom the Rivian will be the first electric car: YMMV!

For fun I fit a polynomial to the data which picks up both the inertial and drag loads pretty well. I then plotted the v-squared term separately as the dotted green curve. This suggests that drag will become noticeable at about 60 mph (where I estimate it will steal 15% of my range) and dominate above say 70. At 100 mpH I estimate, from these data, that it would eat half.

I know not many here are conversant with manipulation of data sets of this sort so I include the caveat that these data are at best representative. You will not find your R1T or R1S turning in data identical to this. Just be aware that high speed will eat your lunch. I wonder that the Germans buy these things (I assume there are still some frei fahren portions of the autobahns).
 

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I think EPA ranges are good for comparing one vehicle to another with an average mix of driving conditions. However, the more one's driving deviates from EPA test methodology, the less reliable the EPA rating becomes.

For instance, Lucid Motors is claiming they have attained well over 400 miles of range in "real world highway" driving. They obtained these figures in a drive down the Pacific Coast Highway from San Francisco to Los Angeles. However, anyone who knows that highway knows that average speeds are much lower than on an interstate. On the other hand, they returned from Los Angeles to San Francisco driving the 70-mph speed limit on the I-5 and completed that 400+ mile leg on a single charge, too. That car, though, just tested at 0.21 Cd for aerodynamics, a far lower figure than I suspect Rivian will attain, coupled with a significantly smaller frontal surface area.

I don't understand the engineering, but Lucid says they have optimized the electronics of the drivetrain for distance driving at speed which will somewhat lessen the likely EPA rating where other driving conditions are mixed in, whatever that means.

While the Lucid Air and Rivian products will probably all get at least a 400-mile range rating in EPA testing with their largest battery packs, I have a suspicion that the Lucid will get far closer to that putative range driving on an interstate than a Rivian will.
 

ajdelange

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I think EPA ranges are good for comparing one vehicle to another with an average mix of driving conditions.
That is, after all, what they are intended for.

I don't understand the engineering, but Lucid says they have optimized the electronics of the drivetrain for distance driving at speed which will somewhat lessen the likely EPA rating where other driving conditions are mixed in, whatever that means.
An electric motor has an efficiency sweet spot. Usually the drive train is geared to put this point at about 45 mph as that gives the best overall EPA rating. But if you change the gearing slightly so that this sweet spot falls at 70 mph that is where the car will be most efficient at the expense of efficiency at lower speeds. That is not to say this is what Lucid has done as, of course, I haven't a clue about that. It is an example of something they could have done which would explain this claim.
 

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An electric motor has an efficiency sweet spot. Usually the drive train is geared to put this point at about 45 mph as that gives the best overall EPA rating. But if you change the gearing slightly so that this sweet spot falls at 70 mph that is where the car will be most efficient at the expense of efficiency at lower speeds.
For the vast majority of EV drivers, especially those who can charge at home for local driving, range becomes an issue primarily in long-distance highway driving.

Trading away some low-speed efficiency to gain more highway range would seem a very desirable trade-off to most buyers of EVs, I would think. However, by lowering the EPA rating in comparison to other EVs, that would also make such an EV look less attractive to an uninitiated buyer.

Maybe Lucid, with all the stress it's putting in its communications about "real world highway" range, is trying to head off this perception problem.
 

ajdelange

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Some very good points there. Here's the obvious solution:

PorscheGB.png


In case you don't recognize it it's the gearing from the Taycan. There are some interesting articles on the design of the car which touch on the issues you raised.

There is, of course, an obvious down side in terms of added weight, complexity and, especially, reliability. Evidently Tesla started out with something like this in mind but dropped it.
 

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Unlike Tesla, the Taycan uses a two-speed transmission, which may be one of the reasons Taycans are getting significantly better range than their EPA rating in extended driving. Lucid is going to use an epicyclic transmission, but I don't know anything about their gear ratios.

In one of the lengthy interviews of Peter Rawlinson (Lucid CEO and Chief Engineer for the original Model S), Rawlinson said something about the inverter electronics having something to do with the extended road range of the Lucid Air, but he didn't go into any detail. (I probably wouldn't have understood it, anyway.)

A lot of Tesla fans are crowing about Tesla's beating Lucid to the 400-mile punch with its new 402-mile EPA range rating. What they overlook is that only the Long Range version of the Model S attained that figure. The Performance version still has a range rating of 348 miles. Lucid is claiming "over" 400 miles of range with a car that matches the Performance version of the Model S. Of course, Tesla is currently using a 100-kWh battery pack where Lucid is using a 110-kWh pack. I suppose it will really come down to the mile/kWh figures of the two cars.

On that score, Lucid is claiming they have hit or exceeded the 4 miles / kWh mark with the Air, a figure that Tesla attains only in the smaller and presumably lighter Model 3 (at 4.1 m/kWh). Lucid is using a 110-kWh battery pack in the beta cars turning in those figures. In the video of the range test that was run from San Francisco to Los Angeles and back on two charges, they stopped outside of San Francisco to pick up Rawlinson for the final leg across the Golden Gate bridge. If you listen very carefully, you can hear him in the background congratulating the guys for covering "almost one thousand miles" on the test run. I don't know whether he meant to be heard (it sounded as if he was speaking before he got into the car where the microphone was) or what he meant by "almost", but it does suggest that Lucid is going to be a good highway driver.

That test was run with two engineers in the car but without a fully fitted-out interior. Lucid says subsequent tests were run with ballast to match the weight of a production car with two passengers and, with subsequent software tweaking, the cars are still matching those range figures on the highway.
 

ajdelange

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Unlike Tesla, the Taycan uses a two-speed transmission, which may be one of the reasons Taycans are getting significantly better range than their EPA rating in extended driving.
Well yes. That's the point I was trying to make in posting a picture of the Taycan transmission.
 

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For fun I fit a polynomial to the data which picks up both the inertial and drag loads pretty well. I then plotted the v-squared term separately as the dotted green curve. This suggests that drag will become noticeable at about 60 mph (where I estimate it will steal 15% of my range) and dominate above say 70. At 100 mpH I estimate, from these data, that it would eat half.
Your numbers are similar to my experience with the Bolt. Here are some ranges I have actually seen on long trips, my EPA rating, which is combo of city highway is 238, but as you state this can vary with weather, driving conditions, HVAC, etc. The numbers below are all with AC on.

65mph trip - 215 miles (10% loss of EPA range)
75mph trip - 190 miles (20% loss of EPA range)
100mph trip (75 speed + 25 wind) - 170 miles (30% loss of EPA range)

I am actually surprised the 100 mph case was not worse, but part of that rip was 65mph in the city and not directly into a headwind before hitting the open road.
 

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Well yes. That's the point I was trying to make in posting a picture of the Taycan transmission.
Earlier on, I saw an interview with a Lucid engineer in which it was said that Lucid was going to use a cycloidal transmission. A more recent interview with Rawlinson had him stating they were using an epicyclic transmission. Thinking they might be two different terms for the same design, I did a little internet digging and found they are significantly different in design and application, although both have certain advantages over conventional automobile transmissions.

Rawlinson has said that Lucid's 600-hp motor, inverter, and transmission have a combined weight of 160 pounds and yield the most volumetric efficiency of any EV drive unit.

What's your take on this?
 

ajdelange

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Your numbers are similar ....
"Similar" is the word I'd like to emphasize the most strongly. Your results better be similar to mine because we are subject to the same physics. But we are using sampled data from a set where things can vary widely dependent on driving style, weather, road surface condition, terrain etc. When I predict that I'd lose 48% of my range driving at 100 mph that is just that - a prediction and predictions come with uncertainty. We have ways of quantifying that uncertainty and I'll do that but I'll just point out that predicting what will happen at 100 mph from a data set than ends at 62 mph is what one colleague used to call "bold extrapolation". I once witnessed an old, respected university professor (from my Alma Mater, yet) just destroy a young man from overseas when he presented data using "bold extrapolation" at a professional society meeting. But it is OK to do it if you understand what you are doing.

So here's my drive history again with the curve fit to the data.
TeslaDrivesY.jpg


But this time there are dashed line curves on either side of the best fit curve. These are the 90% confidence limits. IOW the actual Wh/mi at 100 mph lies between 339 and 659 Wh/mi with 90% probability based on the quality and quantity of the data I have. The way to improve the quality of the estimate is to get more data and have more of it at higher speeds. But that's what statistics is all about: drawing reasonable conclusions from the limited data you have.
 

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